1. Field of the Invention
The present invention relates generally to spirometers. Spirometers are devices used to measure lung capacity and other functions of the lungs in patients with various pulmonary disorders. More particularly, the invention relates to a filtration device for spirometers which is placed between the patient and the spirometer to avoid contamination of the spirometer by mucous droplets exhaled by the patient. Most particularly, the present invention relates to a reinforced filter media, and a filtration device using the same, for use by the patient with the Spirometer to prevent the aforementioned contamination problem.
2. Description of Prior Art
Researchers are currently looking for accurate methods to predict a person's chances of developing various airway obstructions. These obstructions are sometimes called chronic obstructive pulmonary disease (COPD). None of the current ways used to diagnose COPD detects the disease before irreversible lung damage occurs. While many measures of lung function have been developed, those most commonly used determine: 1) air containing volume of the lung (lung volume), 2) the ability to move air into and out of the lungs, 3) the rate at which gas is defused between the lung and the blood, and 4) blood levels of oxygen and carbon dioxide.
Lung volumes are measured by breathing into and out of a device called a spirometer. Some types of spirometers are very simple mechanical devices which record volume changes as air is added to or removed from them. Other kinds of spirometers are more sophisticated and use various types of electronic equipment to determine and record the volume of air moved into and out of the lungs. Three volume measures most relevant to COPD are forced vital capacity (FVC), residual volume (RV), and total lung capacity (TLC). The forced vital capacity is the maximum volume of air which can be forcibly expelled after inhaling as deeply as possible.
Not all of the air in the lungs is removed when measuring the vital capacity. The amount remaining is called the residual volume. The total lung capacity is the combination of the forced vital capacity and residual volume. While most of the measured lung volumes or capacities change to some degree with COPD, residual volume usually increases quite markedly. This increase is the result of the weakened air ways collapsing before the normally expired air can leave the lungs. The increased residual volume makes breathing even more difficult and labored.
Because COPD results in narrowed air passages, a measure of the rate at which air can be expelled from the lungs can also be used to determine how severe the narrowing has become. In this test, the forced vital capacity maneuver, the patient is asked to inhale as deeply as possible and, on signal, exhale as completely and as rapidly as possible. The volume of air exhaled within one second is then measured. This volume is referred to as the forced expiratory volume in one second (FEV1). When FEV1 is used as an indicator as lung function, the average rate of decline in patients with chronic obstructive lung disease is observed to be two or three times the normal rate of 10-30 ml per year. This volume may also be expressed in terms of the percent of the vital capacity which can be expelled in one second. As COPD progresses, less air can be expelled in one second. A greater than expected annual fall in FEV1 is the most sensitive test for COPD and a fairly good predictor of disability and early death.
Another measure of lung function is called the fusing capacity. For this, a more complicated test determines the amount of gas which can move in a given period of time from the alveolar side of the lung into the blood. A number of conditions can cause the defusing capacity to decrease. However, in COPD the decrease is the result of the destruction of the alveolar walls which leads to a significant decrease in surface area for defusion of oxygen into the blood.
Because the primary function of the lung is to remove carbon dioxide from the blood and add oxygen, another indicator of pulmonary function is the blood levels of oxygen and carbon dioxide. As chronic obstructive pulmonary disease progresses, the amount of oxygen in the blood decreases and carbon dioxide increases.
In most cases it is necessary to compare the results of several different tests in order to make the correct diagnosis, and to repeat some tests at intervals to determine the rate of disease progression or improvement. Measurement of the FEV1 and FEV1/FVC ratio is becoming a routine part of the physical examination of every patient suspected of having COPD.
It can be easily understood that testing of patients for potential COPD is increasing the use of spirometers. The increased use of spirometers has developed the problem of how to prevent the contamination of the spirometers between tests so as to avoid a lengthy and expensive cleaning procedure between patient tests and the resulting costly downtime of the spirometers.
One attempted solution to the problem of preventing contamination of the spirometer devices has been to insert an in-line filter between the mouthpiece used by the patient to blow into the spirometer and the flexible tube connecting the mouthpiece to the spirometer. The number 3420 Pulmoguard PFT filter distributed by Vacumetrex of Ventura, Calif. is one example of such a filter. The Pro-tec.TM. barrier filter manufactured by Pall Biomedical Products Corporation of Glencove, N.Y. is another example of an in-line filter. These are disposable filters which have been proven to be efficient and do prevent contamination of the spirometers. However, they add substantial cost to the overall expense of testing the ever growing number of patients being tested for COPD and thus they have not been an entirely satisfactory solution.
Another attempt at solving the problem of contamination has been to combine a bag or sock filter with the mouthpiece commonly used by the patient in connection with a spirometer test. Such a combination mouthpiece filter is manufactured by the Mallincrodt Medical Company of Mirandola, Italy. While this has been a generally satisfactory solution to the problem, as it eliminates contamination of the spirometer, and does not involve the increased cost of the disposable in-line filter, when such a combination mouthpiece/filter is used in certain tests, such as the FEC test where the patient is asked to inhale as deeply as possible, the filter media used in the mouthpiece/filter has become dislodged from its normal position within the mouthpiece, and has been sucked into the patient's mouth. Thus, this has also not been an entirely satisfactory solution to the problem of avoiding contamination of spirometers. Thus, those skilled in the art continue to search for a satisfactory method of eliminating the contamination problem in Spirometers during testing for COPD and other various pulmonary disorders.